Ruby on the Modern JVM with JRuby

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Ruby on the Modern JVM

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Who Am I • Charles Oliver Nutter • @headius(@mastodon.social) • headius@headius.com • JRuby developer since 2004 • Full-time JRuby and JVM language advocate since 2006

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What is JRuby? • Ruby on the Java Virtual Machine (JVM) • Ruby implementation fi rst, JVM language second • Many bene fi ts from JVM ecosystem • Ruby code should "just work" • Different extension API, no forking, parallel threads • Thousands of production users, 17+ years of real-world use

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What Is Important? • Usability: compatibility, startup time, warmup time • Runtime: GC, JIT, monitoring, pro fi ling, concurrency • Platform: mobile, server, desktop, integration, deployment • Performance: straight line, scaling, parallelism, resource usage • Approachable: easy to contribute with any level of experience • Different applications needs different things

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Getting Started

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JRuby Install • Install a JDK • Latest Java recommended (Java 21 is LTS) • Java 8 supported for 9.4 and lower • Install JRuby • Recommended: Ruby installer, system package, Docker image • Download tarball/zip or Windows installer

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Test it out! [] ~ $ rvm use jruby Using /Users/headius/.rvm/gems/jruby-9.4.5.0 [] ~ $ irb >> runtime = java.lang.Runtime.runtime => # >> runtime.available_processors => 8 >> runtime.free_memory => 91420584 >>

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Ruby Compatibility • JRuby 9.4 is Ruby 3.1 compatible • 98% of language specs passing • Nearly complete core + stdlib features from 2.7, 3.0 and 3.1 • JRuby 9.3 (Ruby 2.6 compat) maintaned through 2023 • Compatibility before performance!

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JRuby Architecture

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JVM Language • JRuby defers many hard problems to the JVM platform • Native threading and VM internals • Memory management and garbage collection • Native JIT and optimizations • JRuby is a little VM on top of a big VM

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JRuby Compiler Pipeline Ruby (.rb) JIT Java Instructions (java bytecode) Ruby Instructions (IR) parse interpret interpreter interpret C1 compile native code better native code java bytecode interpreter execute C2 compile Java Virtual Machine JRuby Internals

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JVM JIT • HotSpot JIT is most widely deployed • Multi-tier optimizations, fast and stable • Battle-tested for 20 years, dozens of contributors today • Graal JIT: newer, more aggressive optimizations • OpenJ9 JIT (IBM JDK): of fl ine AOT, JIT servers, checkpointing

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Indy on Java 8, 11, 17 Times faster than JRuby Java 8 no indy 0 1.25 2.5 3.75 5 Mandelbrot Red/Black 4.05x 3.92x 3.74x 3.68x 3.72x 1.97x Java 8 indy Java 11 indy Java 17 indy 3.28x CRuby JIT 1.86x CRuby JIT

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Indy + Graal JIT Times faster than JRuby Java 8 no indy 0 4 8 12 16 Mandelbrot Red/Black 3.13x 15.7x 4.05x 3.92x 3.74x 3.68x 3.72x 1.97x Java 8 indy Java 11 indy Java 17 indy Graal CE indy Escape analysis But not always better

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JVM GC • Many options to tune JVM GCs • Heap size: small or large? • Throughput: faster allocations or shorter pause times? • Working set: large in-memory or mostly new objects? • Many options in standard OpenJDK • Serial, Parallel, G1, ZGC, Shenandoah, MMtk

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Visual VM

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Core and Standard Library • Core class like String and Array mostly "native" Java • Small pieces moving to Ruby over time • Standard library largely shared with CRuby • Pure-Ruby libraries are the same (rss, rake, rubygems...) • Extension libraries have JRuby versions (digest, psych, json...) • Many thanks to @hsbt and others for working with us!

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Key Parts of JRuby Ruby parser Compiler and IR Core classes Standard library Java Native/C Ruby

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Key Parts of CRuby Ruby parser Compiler and IR Core classes Standard library Native/C Ruby Rust

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Monitoring and Pro fi ling • VisualVM: GUI console for basic JVM monitoring • JDK Flight Recorder: always-on monitoring with pro fi ling options • Low-overhead 1% to 5%, built into OpenJDK • JDK Mission Control: GUI client for Flight Recorder data • https://adoptium.net/jmc/

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Many Ways to Contribute • Wide array of languages (Java, Ruby, Kotlin, Scala, Clojure, C...) • Straightforward codebase (RubyString, RubyArray, etc) • Many levels of complexity (simple methods up to compiler optz) • Non-coding options (run tests, report issues, try things out) • We need your help!

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Performance and Scaling

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Scaling Applications • Classic problem on CRuby/MRI • No concurrent threads, so we need worker processes • Processes duplicate runtime state and waste resources • JRuby is an excellent solution • Multi-threaded single process runs your entire site • World-class GC uses resources better

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Baseline Rails App • Scaffolded "blog" application on PostgreSQL, Puma • IBM VPC instance: 8 vCPU, 32GB • CRuby 3.2, 16 workers • JRuby 9.4: 16 threads • Database, siege benchmark driver on same instance

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Requests per second 0 450 900 1350 1800 60s siege iteration 1 2 3 4 5 6 7 JRuby CRuby 3.2 CRuby 3.2 + YJIT

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requests per second (higher is better) 0rps 450rps 900rps 1350rps 1800rps 1,550rps 1,280rps 1,705rps JRuby 9.4 CRuby 3.2 CRuby + YJIT

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Memory • JRuby: 3.4GB RSS • JRuby with 300MB heap: 955MB RSS • JRuby G1: 1.6G • CRuby: 16x 103MB = 1.6GB • CRuby YJIT: 16x 125MB = 2GB

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requests per second (higher is better) 0rps 450rps 900rps 1350rps 1800rps 1,643rps 1,550rps 1,280rps 1,705rps JRuby 9.4 CRuby 3.2 CRuby + YJIT JRuby 300MB heap

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RPS per MB of memory (16-way concurrency) 0rps/mb 0.45rps/mb 0.9rps/mb 1.35rps/mb 1.8rps/mb 1.72 rps/MB 0.775 rps/MB 0.8 rps/MB 0.501 rps/MB JRuby 9.4 CRuby 3.2 CRuby + YJIT JRuby 300MB heap

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RPS per MB of memory (160-way concurrency) 0rps 3.5rps 7rps 10.5rps 14rps 13.692 rps/MB 0.775 rps/MB 0.8 rps/MB 4.871 rps/MB JRuby 9.4 CRuby 3.2 CRuby + YJIT JRuby 300MB heap $$$$

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GUIs, Graphics, and Games

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GUI Libraries • Swing, built into JDK • Clean, cross-platform, easy to build simple UIs • Scalable Windowing Toolkit (Eclipse SWT) • Native widgets, WebKit browser component, rich ecosystem • JavaFX (via JRubyFX, github/jruby/jrubyfx) • Scene-based, vector drawing, event-driven modern UI library

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Shoes 4

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Glimmer • Glimmer GUI DSL • Multiple backends (SWT, GTK, ...) • JRuby + SWT is the most mature • JRuby makes cross-platform GUI much easier! • Works same everywhere • GUI libraries shipped with gem

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JRubyFX • JRuby wrapper for JavaFX • Supports FXML layout or direct widget scripting • Deployable on mobile (Android)

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Fun Stuff event(:player_egg_throw) do |e| e.hatching = true e.num_hatches = 120 e.player.mesg "hatched" end Purugin https://github.com/enebo/Purugin

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GUIs... like Android?

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Ruboto: JRuby on Android • ruboto.org, https://github.com/ruboto/ruboto • Actively used for commercial projects today • Build interface with GUI builder, wire it up with Ruby code • Neglected a bit but being updated for JRuby 9.4 now!

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Ruboto IRB • IRB in JRuby on Android! • Plus an editor and script runner • Not currently in the store, but we will republish soon! • Search for "Ruboto Core" and "Ruboto IRB" APKs

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Updated Ruboto! • We are updating Ruboto! • JRuby 9.4, with Ruby 3.1 support • Latest versions of Android • Still a few bugs to work through • https://github.com/ruboto/JRuby9k_POC • jruby_9_4 branch • bundle install ; rake assemble

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Advanced JVM Features

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Fibers

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Fibers • "virtual threads", "threadlets", "coroutines" • Threads depend on OS/CPU to switch contexts • Fibers explicitly switch to another call stack on same Thread • Switch automatically at IO or lock boundaries • Many fi bers to one OS thread, so fewer resources needed • See Vishwa and Ishani's concurrency talk!

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Thread 2 Fiber 2 Fiber 1 hands o ff to Fiber 2, which runs immediately etc Execution fl ow Fiber 1 Wait for IO Accept socket Wait for IO Accept socket Handle request Send response etc Thread 1 Wait for IO Accept socket Thread gets descheduled from CPU but still waiting for IO Handle request Send response

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Fibers on JRuby • No native JVM fi bers, so we have to simulate it with threads! • Very resource-intensive • No more than a couple thousand fi bers at a time • Slow context-switching, at the mercy of OS/CPU • Ruby world moving toward tens of thousands of fi bers...

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5.times do t = Time.now # create 100k fibers ary = 100_000.times.map { Fiber.new { } } # resume and complete 100k fibers ary.each(&:resume) p Time.now - t end

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$ jruby fiber_test.rb [7.603s][warning][os,thread] Attempt to protect stack guard pages failed (0x00007fc240a00000-0x00007fc240a04000). # # A fatal error has been detected by the Java Runtime Environment: # Native memory allocation (mprotect) failed to protect 16384 bytes for # memory to guard stack pages # # An error report file with more information is saved as: # /home/headius/work/jruby93/hs_err_pid75149.log # # If you would like to submit a bug report, please visit: # https://bugreport.java.com/bugreport/crash.jsp # Aborted (core dumped) 😩

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Project Loom • Thread-based fi bers don't scale • Enumerators use fi bers • Structured concurrency is coming • Loom brings fi bers to JVM • Easily handles thousands of fi bers • Faster context-switching

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$ jruby -J--enable-preview fiber_test.rb 2.324123 0.880373 0.6916289999999999 0.73703 0.655856 🤩

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C100k on JRuby? • See @ioquatix talks on async and falcon! • Just starting to add support for io-event, async-io in JRuby • Fiber scheduler and Buffer APIs available now • Great way to contribute!

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Native Libraries

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Ruby and C • Native libraries go hand-in-hand with Ruby • Many extensions written directly to internal APIs • More and more moving to FFI or Fiddle without C code • JRuby needs to support as much as possible • Extensions must be ported to Java (or Ruby) • FFI and Fiddle supported and strongly recommended

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User Code JNR stub JNI call JNI impl libf f Target Library Java C/native

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Project Panama: FFI for JVM • Foreign function interface (FFI) • With JVM help to make direct calls • Foreign memory API • JVM-assisted access, lifecycle • API extraction from C/++ headers • Save time setting up bindings

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User Code Panama stub Target Library Java C/native

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SQLite JDBC Adapter • Java DataBase Connectivity (JDBC) wrapper around SQLite • Used by JRuby for ActiveRecord, Sequel • Java Native Interface (JNI) currently, limits throughput • Proof-of concept Panama-based version working now • Early results: 2x performance

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Prism Parser • Simple C library for parsing Ruby that we can share • JRuby already integrating it! • Nearly all nodes implemented, most code runs today • 20% faster startup • Using JNI/JNR now, will be faster with Panama

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JRuby Future • JRuby 9.4 continues to stabilize • Moving toward maintenance mode • Lots of new JVM features to leverage • Very exciting time for (J)Rubyists! • Big announcement for the fi rst time today...

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JRuby 10 is coming soon!

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JRuby 10! • Major leap forward • Ruby 3.4 support, Java 17 (or 21) minimum • New Prism parser with complete language features • Targeted optimization across the board • Our biggest jump since JRuby 9000 (9.0.0.0) • Now is the time to contribute! 𝕏

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Help Build JRuby 10 • Implement Ruby 3.2, 3.3, 3.4 features (even in Ruby!) • Test libraries, applications and report issues • Triage reported bugs, con fi rm or reject or help fi x • We are standing by to work with you! • https://github.com/jruby/jruby

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Thank You! • Charles Oliver Nutter • headius@headius.com • @headius(@mastodon.social) • https://github.com/jruby/jruby • https://www.jruby.org • JRuby room on [matrix]